it depends on the network

networks like bitcoin and nostr get more decentralized as more people run fully validating nodes (or relays in the nostr-verse) and make conscious choices about which new proposals they will enforce

a network like lightning is a bit different because lightning nodes do not control user funds, so it can be decentralized in that respect even if few people run their own lightning node

but that's nuanced too because custodial solutions are so popular on lightning that it has a whole different kind of decentralization problem -- e.g. it's not decentralized in the way that matters if everyone's just using wallet of satoshi